Fix link in SECURITY.md (#84877)

SECURITY.md

@@ -16,7 +16,7 @@ We use GitHub's security advisory feature to track open security issues. You sho
 a close collaboration as we work to resolve the issue you have reported. Please reach out to
 `security@flutter.dev` again if you do not receive prompt attention and regular updates.
 
-You may also reach out to the team via our public [Discord] chat channels; however, please make
+You may also reach out to the team via our public [Discord](https://github.com/flutter/flutter/wiki/Chat) chat channels; however, please make
 sure to e-mail `security@flutter.dev` when reporting an issue, and avoid revealing information about
 vulnerabilities in public if that could put users at risk.